1. Field of the Invention
The present invention relates generally to scan mechanisms for rotationally positioning a mirror or a light source. More particularly, the present invention relates to a scan mechanism in which a reaction mass balances the rotational mass of the rotationally positionable platform to provide a reactionless scan mechanism.
2. Description of the Related Art
Scan mechanisms are used for various purposes, such as reading bar codes. In such devices, a pivotally mounted platform is rotationally positioned by an electric motor. As the platform is rotationally positioned, a mirror or a light source attached to the platform is scanned across a field with encoded information, thereby cooperating with either the light source or the mirror to read the encoded information.
The prior art includes Weber, U.S. Pat. No. 3,612,643, issued Oct. 12, 1971. Weber provided a scan mechanism in which a mirror, rotatably positioned on bearings, is driven by a rotary motor and a belt.
Dostal, U.S. Pat. No. 3,532,408, issued Oct. 6, 1970, teaches a scan device in which the mirror is mounted on a torsionally deflectable member, pole pieces are attached to opposite sides of the mirror, and field coils are attached to a frame of the device.
Chandler, in U.S. Pat. No. 4,782,475, issued Nov. 1, 1988, teaches a scan mechanism in which the optical element of a read head is supported by a four-member flexure structure, one portion of the motor is attached to the read head, and another portion of the motor is attached to the frame of the mechanism. The four-member flexure structure includes first and second supporting elements that are attached at opposite ends thereof and that cross proximal to the middle of each of the flexure elements.